Additional file 1: of Insights into the segmental identity of post-oral commissures and pharyngeal nerves in Onychophora based on retrograde fills

Scenario on the evolution of the arthropod brain. Animation, swf file. Anterior is up. The compound brain of arthropods (sensu Richter et al. [5]) most likely evolved by a fusion of initially separate proto-, deuto- and tritocerebral ganglia. Note that the tripartite brain of arthropods alternatively might have evolved several times independently, as some groups, including branchiopod crustaceans, show a bipartite brain (e.g. [29]).